1. Field of the Invention
This invention relates to a facsimile apparatus which performs communication after encrypting communication information. Different types of encrypting devices may be connected to such facsimile apparatus. The invention also relates to a method of controlling such facsimile apparatus.
2. Description of Related Art
The most significant feature of ordinary facsimile communication is that it is performed through a transmission control procedure in accordance with CCITT advisory T.30 and enables communication with other facsimile apparatuses via a public telephone network. However, for some users, such as governmental offices and banks, it is necessary that the contents of facsimile communications be kept confidential because of the nature of the work carried out. In order to maintain the confidentiality of such communications, the conventional practice is to connect an encrypting device to the facsimile apparatus. Such a device encrypts the contents of a communication before transmission in order to prevent the leakage of information if the apparatus is inadvertently connected to a facsimile apparatus other than that intended, for example, by dialing the wrong number, or if the telephone line of the apparatus is wire-tapped.
In a case where an encrypting device is connected to a facsimile apparatus and an encrypted communication is transmitted, an operating instruction, which differs depending upon the type of encrypting device, must be designated by using a button on the control panel of the facsimile apparatus. However, this procedure leads to the following difficulties:
(1) Before operating the apparatus, the operator must verity that the connected encrypting device is of the type which includes both a modulator/demodulator circuit and an NCU. This places an increased burden upon the operator.
(2) The control panel of the facsimile apparatus must be provided with an external connection button, which indicates that a modulator/demodulator and an NCU are external devices, thereby allowing an encrypting device of a different type to be connected to the facsimile apparatus. If the operator mistakenly presses this button, encrypted communication will no longer be possible.
(3) The internal control procedure must be changed depending upon the state of the external connection button. This necessitates more complicated software for the facsimile apparatus.